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Energy and the EarthAOSC 200

Tim Canty

Class Web Site: http://www.atmos.umd.edu/~tcanty/aosc200

Lecture 08Sep 19 2019

Topics for today:

• Energy absorption• Radiative Equilibirum

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The energy from the Sun peaks at 0.5 m (the visible portion of the spectrum)The energy from the Earth peaks at 10 m (in the infrared portion)

Fig 2.10: Essentials of Meteorology

Solar Spectrum

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Energy Transfer: Radiation

Copyright © 2014 University of Maryland.

Radiative Heat – heating due to electromagnetic radiation (waves of energy that move through space

Can be:

• Absorbed• Reflected• Scattered

Fig 4.4 Weather: A Concise Introduction

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Albedo

http://marineecology.wcp.muohio.edu/climate_projects_04/snowball_earth/web/WebpageStuff/albedo.html

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Reflection: Albedo

Albedo – the percentage of radiation that is reflected off of a surface

100% means everything is reflected

Snow has an albedo of 90%

Overall, the Earth’s albedo is 30%

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Reflection: Albedo

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What color is the sky?

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What color is the sky?

N2 and O2 are really good at scattering shorter wavelengths

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What color is the sky?

Fig 4.2.1 Weather: A Concise Introduction

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What color is the sky?

Fig 4.2.2 Weather: A Concise Introduction

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How does energy interact with the atmosphere?

The atmosphere absorbs energy only at certain wavelengths and transmits at othersThis figure shows what percentage of energy

is able to travel through the atmosphere Fig 4.6 Weather: A Concise Introduction

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Atmospheric Absorption

The Sun releases energy at shorter wavelengths (UV, visible, near-infrared)

The Earth releases energy at longer wavelengths (IR)

Fig 2.10, 11: Essentials of Meteorology

Abso

rptio

n (%

)

Absorption is the opposite of transmittance

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Atmospheric Absorption

Incoming Solarradiation

Outgoing Terrestrial (Earth)radiation

Fig 2.11: Essentials of Meteorology

Abs

orpt

ion

(%)

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Atmospheric AbsorptionThis slide shows how much radiation is absorbed by the atmosphere at different wavelengths. Example, at 0.1 m the atmosphere absorbs 100% of the incoming radiation from the sun.

Fig 2.11: Essentials of Meteorology

Abs

orpt

ion

(%)

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Atmospheric Absorption from O2 and O3

Fig 2.11: Essentials of Meteorology

Abs

orpt

ion

(%)

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Atmospheric Absorption from CH4

Fig 2.11: Essentials of Meteorology

Abs

orpt

ion

(%)

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Atmospheric Absorption from N2O

Fig 2.11: Essentials of Meteorology

Abs

orpt

ion

(%)

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Atmospheric Absorption from CO2

Fig 2.11: Essentials of Meteorology

Abs

orpt

ion

(%)

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Atmospheric Absorption from H2O

Fig 2.11: Essentials of Meteorology

Abs

orpt

ion

(%)

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Earth without the Greenhouse Effect

Fig 2.12a: Essentials of Meteorology

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Earth with the Greenhouse Effect

Fig 2.12b: Essentials of Meteorology

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Earth with the Greenhouse Effect

Fig 4.7: Weather: A Concise Introduction

What happens when the “blanket gets too thick?

23

Energy Budget cont.

We’ve discussed the composition of the atmosphere.&.

How energy is transferred throughout the atmosphere

.

.

.Now we’ll discuss how composition and the seasons

affects surface temperature

(I know….I’m excited about this, too!!!)

24

Solar Zenith Angle

Fig 2-13 Meteorology: Understanding the Atmosphere

Zenith – the point directly over your headSolar Zenith Angle – the angle between the sun and a point directly overhead

Zenith

25

Solar Zenith Angle

The intensity of light reaching the surface decreases as thesun lowers in the sky

As SZA Intensity

Fig 2.21: Essentials of Meteorology

26

Solar energy reaching the Earth’s surface

Sunlight in the tropics is moreintense because the sun is higher inthe sky than near the polar regions.

Less solar energy makes it throughthe atmosphere to the poles thanthe equator.

The polar regions have a higheralbedo than the tropics. Why?

All of these together lead to anenergy imbalance

Fig 4.8: Weather: A Concise Introduction

27

Solar energy reaching the Earth’s surface

Sunlight in the tropics is moreintense because the sun is higher inthe sky than near the polar regions.

Less solar energy makes it throughthe atmosphere to the poles thanthe equator.

The polar regions have a higheralbedo than the tropics. Why?

All of these together lead to anenergy imbalance

Fig 4.9: Weather: A Concise Introduction

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Global Energy Balance

29

The Seasons

Fig 4.11: Weather: A Concise Introduction